Creating a georeferenced raster layer from an image

If you have an image file from a scanned map (for example, a historic map, or one you or a collaborator drew/annotated by hand), you can import it into GIS software and georeference it, which associates each pixel in your image with a geospatial location.

In ArcGIS, you’ll want to start by loading the image you want to georeference. You can add image files from the “Add Data” button. If the image hasn’t been georeferenced, it will probably place it on your map at about zero degrees latitude, zero degrees longitude (in the ocean just west of Africa).

Zoom your map to the approximate area covered by your map image, then click on the “Georeference” button on the “Imagery” tab.

Click “Add Control Points”. You’ll need to select at least three points on the image to georeference it. Ideally, there will be spaced far apart from one another (e.g. near the sides of the image) and will form a triangle (rather than being along a straight line).

Select a point on the image, followed by the corresponding location on the basemap (you may need to turn off the display on the image to see the basemap). Repeat this at least three times. Each time you add a control point the map will shift, rotate, or stretch to minimize the distances between the points on the image and the points on the map.

When you are satisfied with the position of the image, click “Save” and then “Close Georeference.”

Manually creating a layer of data

Once you’ve loaded a georeferenced layer, you might want to features to create a vector layer.

In ArcGIS< you’ll need to start by creating a new feature class. You’ll use the “Create Feature Class” tool from the Geoprocessing toolbox. Specify a name and a geometry type for your new feature class, then click “Run.” You’ll see a new layer added to the contents pane, but it will have no data in it.

Now you can add features to your new feature class. Click the “Create” button on the “Edit” ribbon. In the “Create Features” tool, select the layer you want to add to, and add your features by clicking on the map. When you are done, click the “Finish” button (the green check mark).